Disposable packaging, in particular, packaging cartons used in the fast food industry, must meet certain technical as well as economic criteria. For economic efficiency, such cartons should be cheap to manufacture in bulk quantities. Technically, the packaging must be constructed of a material that is chemically compatible with the foodstuffs being packaged, and not susceptible to show-through of oil or food juices on the outside of the container. Moreover, the packaging must be sturdy enough to allow handling without damage during a high speed forming process, and to permit stacking of the filled cartons. Such packaging is also desirably of a design that allows nesting of the empty formed containers for efficient storage.
Another desirable feature of such disposable packaging cartons is a closure means that can be easily opened and closed. In this regard, several closure means have been reported in the prior art. U.S. Pat. No. 2,956,720 (Rindal) describes a carton having an arrow lock closure consisting of a combination of a horizontal and angled slits forming a slit closure in one panel of the carton, and an arrow-shaped tab on the edge of a panel overlying the panel containing the slit. Closure is effected by pushing the arrow-shaped tab downward and toward the interior of the carton, thereby pressing the slit closure to separate the horizontally placed slits, thus allowing entry of the arrow tab. Because of the manner in which the slit closure is opened, the lower free end of the tab may be displaced appreciably inwardly against the contents of the carton, thereby forming a product-free, pocket-like area which ensures an opportunity for free entrance of the arrow tab.
U.S. Pat. No. 4,516,718 (Forbes) discloses a clamshell container having a positive locking closure. To close this container, the reference teaches engaging one or more upwardly directed tongue elements positioned at the free edges of a tray portion with one or more slit openings, each of which is positioned closely adjacent to a score line between the top panel and a side wall. By this closure means, the locking tongue is extends above and outside the lid when the carton is closed, and thus may be easily displaced by depressing the locking tongue element when it is desired to open the carton.
U.S. Pat. No. 4,763,832 (Forbes) describes a clamshell container with a bottom lock closure, in which the tray component includes at least one locking slot formed by a continuous cut line located in the tray front wall. This locking slot is closely adjacent to a score line that forms the fold between the bottom panel and front wall, and cooperates with a tongue element on the lid component, such that when the lid component and tray component are brought together to close the carton, the tongue element is automatically guided into the locking slot. The closure means is released by pressing inwardly on the front wall of the lid.
While the prior art, as discussed above, has utilized tab and slot closure elements together in disposable containers such as clamshells, in each instance the tab is exposed and is therefore prone to bending, tearing or other deformation during closure, which can compromise the closure means. Typically, the tab or tongue element is a relatively fragile element of the container because of its relatively small surface area and because it is pendent from and unsupported by the container wall from which it is appended. A closure means having a tab element, which can be opened without direct handling of the tab, is thus desirable.
The prior art therefore evidences a need for a positive locking container having a tab and slot combination closure, in which the tab element is less susceptible to tearing or deformation. Such a container should further be easily opened by applying positive pressure to the exterior of the container without direct handling of the tab. Such a container should also be inexpensive to manufacture, and capable of being stored efficiently before and during use.